Numerous compositions of protective coatings of alloys which primarily contain nickel, chromium, cobalt, aluminium and a reactive element of the rare earths have been developed and tested. Such coatings have become known heretofore from U.S. Pat. Nos 4,005,989, or 5,401,307 for example. From U.S. Pat. No. 4,034,142, it is also known that an additional constituent, silicon, can further improve the properties of such protective coatings.
Although the relatively wide ranges of the various elements in these documents, in fact, do suggest qualitatively a way to create protective coatings resistant to high-temperature corrosion, the compositions disclosed are not sufficiently specific quantitatively for all purposes.
German Patent 23 55 674 discloses further compositions for protective coatings, but they are not suitable for uses or applications of the type which can occur with stationary gas turbines having a high inlet temperature.
These protective coatings show a high degree of inner oxidation and therefore the development of cracks, which leads to an ablation of the above laying coating.